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These synchronized galaxies are upending what we know about the universe

Throughout the universe, countless small galaxies rotate around larger host galaxies—our Milky Way has at least a few dozen hangers-on—and theory predicts that they should move randomly. But new research reveals a set of baby galaxies that spin regularly around their host like a carousel. The tiny galaxies surrounding Centaurus A, about 12 million light-years from Earth, were recently found to be orbiting in a surprisingly flat plane—not a random sphere. And if that wasn’t odd enough, new research shows that most of these galaxies are also moving in the same direction. Astronomers sifted through a catalog containing measurements of hundreds of galaxies to find the speed and location of 16 satellites around Centaurus A. They discovered that galaxies on one half of the plane, which is seen edge-on from Earth, tend to be moving toward us, whereas those on the other half are moving away. That suggests they are nearly all rotating in the same direction, the researchers write today in Science. What’s more, the galaxies orbiting both the Milky Way and our nearest neighbor Andromeda also seem to rotate in the same direction and in thin planes. Theoretical models of galaxy formation produce this arrangement less than 0.5% of the time, and the researchers suggest that these planes of satellites might instead be the product of ancient collisions between massive galaxies.